OBJECTIVES: 1. The effects of d-amphetamine on locomotor activity will be tested on 25-day-old rats pretreated with pargyline, desipramine, and 6-hydroxydopamine, to insure substantial depletion of dopamine and minimal depletion of norepinephrine. 2. If the 25-day-olds show no potentiation in activity when treated with amphetamine (as opposed to a reduction in activity), 10-day-old animals will be tested to determine whether this due to the development of an inhibitory system. 3. The roles of cholinergic and serotonergic inhibitory systems will be tested by determining whether treatment with either scopolamine or para-chloro-phenylalanine restores the potentiating effect of amphetamine in 25-day-old animals pretreated with pargyline + desipramine + 6-dydroxydopamine. 4. The extent and location of the degeneration of dopamine systems will be evaluated using regional assays as well as histofluorescent miscroscopic examination.